Passive shunting systems are often subject to functional failures such as over drainage, under drainage or blockage. These can prevent effective treatment and may cause the symptoms of disease to recur. Such shunting systems operate based on physiological pressure gradients and therefore must rely on increasing the shunt diameter to decrease the flow resistance, in order to provide increased flow. Increases in inner diameter however make shunting systems quite bulky. This can make the device less convenient and can lead to patient discomfort.
Issues for an active catheter shunt system may include the method by which fluid is pumped, and miniaturization of the pumping device.
Current miniaturized pumping concepts often operate at high pressures, which can be damaging to the surrounding tissues. A tubular hydroimpedance pump is particularly well suited for applications in biomedicine because it can operate bidirectionally under low pressure, high flow conditions. Examples of such applications include venous valve prosthesis for chronic venous insufficiency, esophageal sphincter valve prosthesis for gastroesophageal reflux disease, shunting prosthesis for hydrocephalus, aqueous drainage shunt for glaucoma, portacaval shunt for treating high blood pressure in the liver, ventriculoperitoneal shunt to relieve cerebrospinal fluid, endolymphatic shunt to relieve the symptoms of vertigo and hearing loss due to endolymphatic hydrops, Blalock-Taussig shunt for aorta-to-the pulmonary artery bypass, and others.
Many different systems available for pumping fluid. These systems commonly use impellers, a set of blades, gears, or pistons in order to transfer the energy to drive the fluid in a specific direction. These systems however involve moving parts which are subject to wear due to friction, ultimately limiting the lifetime of the device. Less conventional pump designs such as peristaltic pumps, or diaphragm pumps are also known. These pumps however rely on the displacement of relatively large surface areas. In a regime where viscous forces are dominant, large machinery is often required to produce the pressure necessary to drive the fluid rendering these concepts unsuitable for applications where the fluid can be damaged or space is limited. In addition, special features to prevent hemolysis are not usually available in the current pump designs.
U.S. Pat. Appl. publication No. 2003/0185692 to Ng et al, discloses a valveless micropump comprising: a hollow pump chamber having a driving element coupled thereto; an inlet channel coupled to the hollow pump chamber; an outlet channel coupled to the hollow pump chamber; the inlet channel, the hollow pump chamber and the outlet channel defining a fluid Flow path through the inlet channel, the hollow pump chamber, and the outlet channel; and at least one direction-sensitive element disposed in the flow path within one of the inlet and outlet chambers, wherein the at least one direction-sensitive element comprises an airfoil.
U.S. Pat. No. 6,254,355 to Morteza Gharib, one of co-inventors of the present invention, the entire contents of which are incorporated herein by reference, discloses a valveless fluid system based on pinch-off actuation of an elastic tube channel at a location situated asymmetrically with respect to its two ends. Means of pinch-off actuation can be either electromagnetic, pneumatic, mechanical, or the like. The hydro-elastic pump therein must have the elastic tube attached to other segments that have a different compliance (such as elasticity). This difference in the elastic properties facilitates elastic wave reflection in terms of local or global dynamic change of the tube's cross-section. This results in the establishment of a pressure difference across the pump and thus unidirectional movement of fluid. The intensity and direction of this flow depends on the frequency, duty cycle, and elastic properties of the tube.
In a copending application U.S. patent application Ser. No. 10/382,721, filed Mar. 4, 2003, a method for pumping fluid is disclosed, comprising: pinching a portion of an elastic element in a way which increases a pressure in a first end member of the elastic element more than a pressure in a second end member of the elastic element without valve action, to cause a pressure differential, wherein the end members have different hydroimpedance; and using the pressure differential to move fluid between the first and second end members. The pinching mechanism is carried out by a device mounted on the exterior surface of the elastic element, which is obstructive in applications.
The elastic wave reflection of a hydro-elastic pump depends on the hydroimpedance of the segments. In the prior art hydro-elastic pump, it was required that the segments to be stiffer either by using a different material or using reinforcement. To overcome the limiting conditions of the prior hydro-elastic pump systems, it is disclosed herein that the pinching location separates two segments with different hydroimpedances, including but not restricted to the characteristic impedance or any impedance in which attenuation occurs over distance, with certain frequency and duty cycle to form asymmetric forces that pump fluid achieving a non-rotary bladeless and valveless pumping operation.